Use Spark or Particle Variables ? Which firmware?

I am using a Core, it flashes from Particle Build with Firmware 3.4,

When writing code should I call Spark Variables or Particle Variables ? Does it matter ?
Does it matter which firmware I use ?

Should I use the firmware 4.9 that shows default ? The dashboard says I am using 3.4


If you’ve got no specific reason to stay on a lower firmware version (and it seems that you don’t), I’d recommend upgrading to the latest, since that’ll have the most new features/bug fixes.
For naming things, go for the ‘Particle’ ones, since that’s what will be supported in the future, while ‘Spark’ will/should be deprecated.